The present invention relates to a solvent-free two-component curable adhesive composition for lamination and a process of lamination. In further detail, the present invention relates to a solvent-free two-component curable adhesive composition for lamination useful in producing materials for packaging food, beverages, medicines, and others, and to a process of lamination.
Composite laminated films comprising metal foil such as aluminum foil have been widely used as materials for packaging food, beverages, medicines, and others. These composite laminated films can be obtained by gluing at least one side of metal foil and a plastic film of any kind together using an adhesive.
To be concrete, when bonding films to the both sides of metal foil, at first, a first plastic film is adhered to one side of the metal foil (first laminating step) and the resultant laminated foil is rolled up. The composite laminated film once rolled up is then paid out, and another plastic film is bonded to the other side of the metal foil (second laminating step). Thereafter, the resultant laminated film is rolled up again. If necessary, in some cases, the laminated metal foil is laminated with still another plastic film (e.g., third laminating step, forth laminating step).
Up to now, an organic solvent-based two-component curable adhesive being the blend of a polyisocyanate compound and at least one member selected from a polyester polyol, a polyether polyol, and a polyurethane polyol has been used as the above-described adhesive for lamination.
In recent years, for improving working environment and as a result of restrictions on the use of solvents, there is a gradual transition from the use of organic solvent-based adhesives to the use of solvent-free adhesives, and adhesive compositions being blends of a polyol component and a polyisocyanate component have come into use as solvent-free adhesives for lamination.
Conventional solvent-free adhesives, however, have the drawback of, when a roll of the laminated film after the first laminating step is left alone, permeating through the minute pinholes of metal foil and causing blocking. This leads to the problem that the composite film breaks while being rolled out or during the second laminating step. The thinner the metal foil (e.g., aluminum foil) is, the higher the rate of occurrence of such trouble is. In addition, a laminating operation under certain conditions (e.g., in the case where the composite film after the first laminating step is rolled up at a higher tension, the case where a solvent-free two-component adhesive is cured at high temperatures, the case where the amount of an adhesive applied is large) is liable to be faced with such problem.
Thus, an object of the present invention is to provide a solvent-free two-component curable adhesive composition for lamination capable of preventing the occurrence of blocking caused by an adhesive seeped through metal foil, and a process of lamination.
Another object of the present invention is to provide a solvent-free two-component curable adhesive composition for lamination capable of preventing the occurrence of blocking even in the case where metal foil such as aluminum foil is thin, and a process of lamination.
Still another object of the present invention is to provide a solvent-free two-component curable adhesive composition for lamination which is, even in the case of lamination under severe conditions, capable of inhibiting the occurrence of blocking, and a process of lamination.
The inventors of the present invention made intensive studies to achieve the above objects, and finally found that the use of a solvent-free two-component curable adhesive composition for lamination, which comprises a polyol component and a polyisocyanate component and has a specific viscosity, inhibits the occurrence of blocking due to the seepage of the adhesive through metal foil. The present invention was accomplished based on the above finding.
That is, the solvent-free two-component curable adhesive composition of the present invention comprises (A) a polyol component and (B) a polyisocyanate component, and the viscosity of the mixture at 80xc2x0 C. immediately after the time the components (A) and (B) are mixed together is not less than 900 mPaxc2x7s. The component (A) may be a polyester polyol which can be obtained from a polyhydric alcohol and at least one member selected from the group consisting of an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid. The number average molecular weight of the component (A) may be not less than 800 (particularly, 800 to 5,000), or the viscosity of the component (B) at 25xc2x0 C. may be not less than 20,000 mPaxc2x7s (particularly, 20,000 to 1,000,000 mPaxc2x7s). The component (B) is at least one member selected from: (B1) a reaction product of a polyisocyanate and at least one member selected from a polyhydric alcohol, a polyester polyol, a polyether polyol, a polycarbonate polyol, and a polyurethane polyol; and (B2) a polyisocyanate derivative. Particularly, the component (B) is one containing a derivative of at least one diisocyanate selected from the group consisting of araliphatic diisocyanates, alicyclic diisocyanates, and aliphatic diisocyanates and may have a plurality of terminal isocyanate groups. The equivalent ratio of the isocyanate group of the component (B) to the hydroxyl group of the component (A) (NCO/OH) is about 0.4 to 10 (particularly, 0.5 to 5). The composition of the present invention may further comprise an adhesion improving agent (particularly, a coupling agent or an oxygen acid of phosphorus, epoxy resin). Moreover, the composition of the present invention may be a composition for laminating metal foil having a thickness of 5 to 15 xcexcm with a plastic film.
The present invention further includes a process for laminating metal foil with a plastic film using the above composition.
Polyol Component (A)
As the polyol component, there can be used at least one member selected from the group consisting of a polyester polyol, a polyether polyol, a polycarbonate polyol, and a polyurethane polyol, etc. There is no particular restriction as to the form (e.g., linear-, branched-chain) of the polyol component provided that the viscosity of the mixture immediately after the time the components (A) and (B) are mixed together is 900 mPaxc2x7s or higher.
The polyester polyol can be obtained through such a conventional esterification reaction as a condensation reaction between a polybasic acid and a polyhydric alcohol, a transesterification reaction between an alkyl ester of a polybasic acid and a polyhydric alcohol, a ring-opening polymerization reaction between a lactone and a polyhydric alcohol and/or a polybasic acid.
Exemplified as the polybasic acid or its alkyl ester are aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanoic diacid, and dimeric acid; alicyclic dicarboxylic acids such as hexahydrophthalic acid and tetrahydrophthalic acid; aromatic dicarboxylic acids such as phthalic acid, isophthalic acid and terephthalic acid; dialkyl esters thereof (e.g., C1-6alkyl esters), and mixtures thereof.
Examples of the polyhydric alcohol are alkanediols (e.g., C2-40 alkane or aliphatic diols of low molecular weight such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, 3,3xe2x80x2-dimetylolheptane, 1,9-nonanediol, 1,10-decanediol, 12-hydroxystearyl alcohol, and hydrogenated dimer diols); polyoxyalkylene glycols (e.g., poly(oxyC2-4alkylene)glycols such as diethylene glycol, triethylene glycol, polyoxyethylene glycol, dipropylene glycol, polyoxypropylene glycol, and polyoxytetramethylene glycol, and copolymers of C2-4alkylene oxides); alkylene oxide adducts of bisphenol A or hydrogenated bisphenol A; polyols (e.g., glycerol, trimethylolpropane, pentaerythritol, sorbitol); and mixtures thereof.
Exemplified as the lactone are C3-14 lactones such as xcex5-caprolactone, xcex4-valerolactone, and xcex2-methyl-xcex4-valerolactone.
Exemplified as the polyether polyol are homo- or copolymers of alkylene oxides (e.g., C2-5alkylene oxides such as ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, 3-methyltetrahydrofuran, and oxetane compounds).
Exemplified as the polycarbonate poloyol is a polycarbonate diol obtained through the reaction between a short chain dialkyl carbonate (e.g., diC1-4alkyl carbonate such as dimethyl carbonate, diethyl carbonate) and at least one member selected from the group consisting of the above-mentioned polyhydric alcohol, polyester polyol, and the polyether polyol.
The polyurethane polyol can be obtained by reacting a polyisocyanate with at least one member selected from the group consisting of the above-mentioned polyhydric alcohol, the polyester polyol, the polyether polyol, and the polycarbonate polyol.
Exemplified as the polyisocyanate are polyisocyanate monomers and their derivatives that are ordinarily employed in the production of polyurethane.
Included among the polyisocyanate monomers are, for example, aromatic diisocyanates, araliphatic diisocyanates, alicyclic diisocyanates, and aliphatic diisocyanates.
Examples of the aromatic diisocyanates are m- or p-phenylene diisocyanate and mixtures thereof, 4,4xe2x80x2-diphenyl diisocyanate, 1,5-naphthalene diisocyanate (NDI), 4,4xe2x80x2-, 2,4xe2x80x2-, or 2,2xe2x80x2-diphenyl methane diisocyanate and mixtures thereof (MDI), 2,4- or 2,6-trilene diisocyanate and mixtures thereof (TDI), 4,4xe2x80x2-toluidine diisocyanate (TODI), and 4,4xe2x80x2-diphenylether diisocyanate.
Examples of the araliphatic diisocyanates are 1,3-, or 1,4-xylylene diisocyanate and mixtures thereof (XDI); 1,3- or 1,4-tetramethylxylylene diisocyanate and mixtures thereof (TMXDI), and xcexa9, xcexa9xe2x80x2-diisocyanate-1,4-diethylbenzene.
Examples of the alicyclic diisocyanates are 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatemethyl-3,5,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate: IPDI), 4,4xe2x80x2-, 2,4xe2x80x2-, or 2,2xe2x80x2-dicyclohexylmethane diisocyanate and mixtures thereof (hydrogenated MDI), methyl-2,4-cyclohexanediisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,3-, or 1,4-bis(isocyanatemethyl)cyclohexane and mixtures thereof (hydrogenated XDI).
As the aliphatic diisocyanates, there are mentioned trimethylene diisocyanate, teteramethylene diisocyanate, hexamethylene diisocynate (HDI), pentamethylene diisocyanate, 1,2-, 2,3-, or 1,3-butylene diisocyanate, and 2,4,4-, or 2,2, 4-trimethylhexamethylene diisocyanate.
Exemplified as the derivatives of polyisocyanate monomers are oligomers (e.g., dimers, trimers) of the polyisocyanate monomers mentioned above; modified oligomers (e.g., modified dimers, modified trimers); modified biuret formed by the reaction of any of the above-mentioned polyisocyanate monomer with water; modified allophanate formed by the reaction of any of the above-mentioned polyisocyanate monomer with a polyhydric alcohol; oxadiazinetrione formed by the reaction of any of the above-mentioned polyisocyanate monomer with a carbonic acid gas.
When the component (A) is a polyurethane polyol, there can be used a terminal hydroxypolyurethane having an equivalent ratio of the isocyanate group of the polyisocyanate component to the hydroxyl group of the polyol component (NCO/OH) of smaller than 1.
Of these polyols, polyester polyols, particularly those that can be obtained from at least one polybasic acid selected from the group consisting of an aromatic dicarboxylic acid (e.g., isophthalic acid, terephthalic acid, and alkyl esters thereof) and an aliphatic dicarboxylic acid (e.g., adipic acid, sebacic acid, azelaic acid), and a polyhydric alcohol (e.g., ethylene glycol, diethylene glycol, 1,4-butanediol, 1,3-butanediol, neopentyl glycol, 1,6-hexanediol) are preferable.
These components (A) can be used either singly or in combination. The number average molecular weight of the component (A) is 800 or more (e.g., 800 to 5,000) and preferably 800 to 3,000 (e.g., 850 to 2,000). If the number average molecular weight is smaller than 800, the components of the adhesive will pass through the pinholes of metal foil, and the film after the first laminating step shows the tendency of blocking. Particularly, when the viscosity of the component (B) at 25xc2x0 C. is smaller than 20,000 mPaxc2x7s, it is preferred that the number average molecular weight of the component (A) is 800 or more. On the other hand, if the number average molecular weight is greater than 5,000, the viscosity becomes too high, and this results in difficulty in coating the composition.
Polyisocyanate Component (B)
There is no particular restriction as to the polyisocyanate component (B) provided that the component (B) has a plurality of terminal isocyanate groups and the viscosity of the mixture at 80xc2x0 C. immediately after the time the components (A) and (B) are mixed together is 900 mPaxc2x7s or higher. Among others, preferred as the component (B) are components containing a derivative (e.g., dimer, trimer, trimers in which part of the NCO group is modified or reacted with a mono- or polyol, a polyisocyanate containing a biuret unit, a polyisoycanate containing an allophanate unit) of at least one diisocyanate selected from an araliphatic diisocyanate (e.g., XDI), an alicyclic diisocyanate (e.g., IPDI), and an aliphatic diisocyanate (e.g., HDI), with components containing a trimer in which the NCO group is partially modified or reacted with a mono-ol (e.g., C1-6alcohols such as t-butanol) or a polyol (e.g., polyols such as alkanediol and polyoxyalkylene glycol) and components containing a biuret unit-containing polyisocyanate particularly preferred. The component (B) may comprise a terminal isocyanate group-containing oligomer (e.g., a reaction product of polyisocyanate and at least one member selected from, e.g., the aforementioned polyhydric alcohols, polyester polyols, polyether polyols, polycarbonate polyols, and the polyurethane polyols). Particulalry, it may comprise a reaction product of a polyester polyol and polyisocyanate.
The terminal isocyanate group-containing oligomer need only have an equivalent ratio of the isocynate group of the polyisocyanate component to the hydroxyl group of the polyol component (NCO/OH) exceeding 1, and the ratio is preferably about 1.5 to 3, more preferably about 1.7 to 3 (e.g., 2 to 2.5).
These components (B) can be used either singly or in combination. The viscosity of the component (B) at 25xc2x0 C. is about 20,000 mPaxc2x7s or higher (e.g., 20,000 to 1,000,000 mPaxc2x7s) and preferably about 20,000 to 500,000 mPaxc2x7s. If the viscosity of the component (B) at 25xc2x0 C. is lower than 20,000 mPaxc2x7s, the components of the adhesive pass through the pinholes of metal foil, and the film shows the tendency of blocking after the first laminating step. Particularly, in the case where the number average molecular weight of the component (A) is smaller than 800, it is preferred that the viscosity of the component (B) at 25xc2x0 C. is 20,000 mPaxc2x7s or higher. With such viscosity, although the number average molecular weight of the component (A) is smaller than 800, the occurrence of blocking is effectively prevented. On the other hand, if the viscosity is higher than 1,000,000 mPaxc2x7s, the possibility of the coating step becoming difficult will arise.
In the present invention, although what is required is only that the number average molecular weight of the component (A) is 800 or greater, or that the viscosity of the component (B) at 25xc2x0 C. is 20,000 mPaxc2x7s or higher, it is preferred that both conditions are met.
The solvent-free two-component curable adhesive for lamination can be obtained by blending the components (A) and (B). The compounding ratio of the component (A) to the component (B) can be selected such that the equivalent ratio of the isocyanate group of the component (B) to the hydroxyl group of the component (A) (NCO/OH) is within the range of about 0.4 to 10, preferably about 0.5 to 5, and particularly about 0.6 to 2.5.
Additive
If necessary, to the adhesive composition of the present invention may be added an additive(s). Exemplified as the additive is an adhesion improving agent of at least one member selected from the group consisting of coupling agents (silane coupling agent, titanium coupling agent, particularly silane coupling agent), oxygen acids of phosphorus (e.g., orthophosphoric acid, metaphosphoric acid, polyphosphoric acid), derivatives thereof, and epoxy resin. The silane coupling agent has at least an alkoxysilyl group (particularly, a C1-2alkoxysilyl group), and may have such a functional group as an isocyanate group, a polymerizable group (e.g., vinyl group, (meth)acryloyl group), a glycidyl group, an N-substituted amino group, carboxyl group, and mercapto group. Examples of the epoxy resin mentioned above are bisphenol-based epoxy resins of A, F, and AD type, bromine-containing epoxy resins, phenol or cresol-based epoxy resins, cyclic aliphatic epoxy resins, glycidyl ester-based epoxy resins, glycidylamine-type epoxy resins, and heterocyclic epoxy resins. Bisphenol-based epoxy resins (particularly, bisphenol A-based epoxy resins) are usually employed. The number average molecular weight of such additive is usually about 700 or smaller, and preferably about 80 to 600 (e.g., 100 to 600).
Further, as an additive, to the composition may be added: a catalyst for controlling a curing reaction; a coatability improving agent; a leveling agent; an antifoaming agent; a stabilizer typified by an antioxidant and an ultraviolet ray absorber; a plasticizer; a surfactant; a coloring pigment; organic or inorganic particulates; and others.
The adhesive composition may incorporate these additives in a proportion of, per 100 parts by weight of the component (A), about 0.001 to 5 parts by weight, preferably about 0.01 to 5 parts by weight. If the amount of the additive(s) used (particularly, total amount) is smaller than 0.001 part by weight, the effects of the additive(s) are hardly shown. If the amount is greater than 5 parts by weight and the additive(s) are of low-molecular weight, the adhesive is drawn into the pinholes along with the additive(s) and passes therethrough, and the film shows the tendency of blocking in the first lamiantion step.
Solvent-Free Two-Component Curable Adhesive Composition For Lamination
The solvent-free two-component curable adhesive composition for lamination of the present invention formed by blending the above-described components can be used in bonding metal foil and a plastic film together with the use of an ordinary laminator for solvent-free adhesives.
The viscosity of the mixture immediately after the time the components (A) and (B) are mixed together at 80xc2x0 C. is about 900 mPaxc2x7s or higher (900 to 10,000 mPaxc2x7s). Preferably, the viscosity is within the range of about 900 to 5,000 mPaxc2x7s, and more preferably about 900 to 3,000 mPaxc2x7s. If the viscosity is too low, the possibility of delamination due to a weak initial cohesive force will arise. If the viscosity is too high, there will arise the possibility of the coating step becoming difficult leading to detraction of the external appearance. Incidentally, the phrase xe2x80x9cimmediately afterxe2x80x9d the mixing means not longer than 5 minutes has passed after the mixing of the components to uniformity.
Process of Lamination
The adhesive composition of the present invention is useful in laminating metal foil with a plastic film. Exemplified as the metal foil is spreadable metal foil (e.g., aluminum foil, gold foil). The thickness of the metal foil is, for example, 5 to 100 xcexcm, preferably about 5 to 20 xcexcm, and more preferably about 5 to 15 xcexcm (particularly, 5 to 10 xcexcm).
Exemplified as the plastic film are films of olefinic polymers (e.g., polyethylene, polypropylene), polyester-series polymers (e.g., polyalkylene terephthalates typified by polyethylene terephthalate and polybutylene terephthalate; polyalkylene naphthalates; and copolyesters of which the main component is any of these polyalkylene arylate units); polyamide-series polymers (e.g., nylon 6, nylon 66); and vinyl-series polymers (e.g., polyvinyl chloride, ethylene-vinyl acetate copolymer). These plastic films may be non-stretched films (non-stretched polyethylene, polypropylene, and others) or stretched films (e.g., biaxially stretched polypropylene, polyalkylene terephthalate, nylon), and either will do. The surface (the surface on which the adhesive composition is applied, or the surface on which the adhesive composition is corona discharge treatment. The surface may be provided with a primer layer of, e.g., an anchor coat agent. Moreover, there may be used a composite laminated film constituted of an extruded film of any kind and the above-described film previously bonded together with another adhesive. The thickness of the plastic film is usually about 5 to 200 xcexcm. The plastic film described above may be one with an image printed thereon.
It is not critical whether one side of the metal foil is laminated with the plastic film or both sides of the metal foil are laminated with the plastic film (second laminating step). Usually, the metal foil is laminated with the plastic film in the first laminating step to be a composite film, and the composite film is rolled up on a batch-up roll and, after being aged if necessary, rolled out for further laminated in the second laminating step. The composite film thus laminated twice is rolled up on a batch-up roll and, if necessary, aged. In the first laminating step, usually, the adhesive composition is applied onto the plastic film and the plastic film is then bonded to metal foil such as aluminum foil. Before being subjected to the second laminating step, the composite laminated film may be heated/aged (e.g., aging at 25 to 60xc2x0 C.) for having the adhesive begin its curing reaction, or the composite film may be subjected to the second laminating step directly without being aged. Blocking tends to occur during the heating or aging step. The adhesive composition of the present invention, however, prevents the occurrence of blocking even if the composite film is heated/aged after the first laminating step. The adhesive composition of the present invention need only be used at least in the first laminating step. An adhesive for use in the second and the following laminating steps may be any adhesive for lamination, and not only solvent-free adhesives but also solvent- or water-based adhesives are also available.
When applying (coating) the adhesive composition, it is preferred that the adhesive composition is heated at a temperature within the range of about 50 to 100xc2x0 C. (preferably, 50 to 90xc2x0 C., more preferably 50 to 80xc2x0 C.) until it acquires a suitable viscosity. The suitable viscosity is, at a given temperature within the above-mentioned range, about 100 to 5,000 mPaxc2x7s and preferably about 300 to 3,000 mPaxc2x7s. If the temperature is above 100xc2x0 C., before being coated, the adhesive composition begins to generate heat as a result of the reaction between the component (A) and the component (B) and gets viscous acceleratingly. This could lead to detraction in external appearance.
The amount of the adhesive composition of the present invention to be applied is, in each laminating step, about 0.5 to 5 g/m2, preferably about 1 to 3 g/m2, and more preferably about 1.5 to 2 g/m2. If the amount of the adhesive composition applied is smaller than 0.5 g/m2, there arise the possibilities that its adhesive properties cannot be fully exhibited and the external appearance becomes poor. Moreover, if the amount of the adhesive composition applied is larger than 5 g/m2, the adhesive seeps from the edge of the film, causing troubles in the production of composite laminated films.
According to the present invention, even when producing a composite laminated film comprising such thin metal foil as aluminum foil with the use of a solvent-free two-component curable adhesive for lamination, it is possible to effectively inhibit the occurrence of blocking due to the permeation of the adhesive through the metal foil.